The conventional active headrest mechanism has a collision load detector provided in a seat back and a coupling mechanism for operatively coupling the detector and the headrest (Patent Documents 1 and 2).
When a rear-end collision occurs and a seated person is moved rearward with respect to the seat back, the detector receives a collision load from the vehicle seat occupant and is moved rearward, and the rearward movement of the detector acts on the headrest through the coupling mechanism to move the headrest forward.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2000-211410
[Patent Document 2] Japanese Patent Application Laid-Open No. 10-138814